Process and apparatus for providing uniform temperature dry-spinning



p 1970 1'. J.. COCHRANE, JR 3,599,244 PROCESS AND APPARATUS FOR PROVIDING UNIFORM TEMPERATURE nny-srxunme Filed Aug. 9, 1967 W; i FIGJ INVENTOR THOMAS J. OOOHRAIE, JR.

AGENT United States Patent O 3,509,244 PROCESS AND APPARATUS FOR PROVIDING UNIFORM TEMPERATURE DRY-SPINNING Thomas J. Cochrane, Jr., Waynesboro, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Aug. 9, 1967, Ser. No. 659,495 Int. Cl. B291? 3/00 US. Cl. 26440 8 Claims ABSTRACT OF THE DISCLOSURE An improvement in the method and means for dry-spinning of continuous filaments which provides a substantially uniform temperature across the spinneret, despite the variable heat pick-up from the hot spinning cell gases, by equalizing the temperature across the extrusion mean-s by the use of a volatile liquid at its boiling point under regulated pressure in channels near the extrusion plate as the heat removal medium.

This invention relates to an improvement in the dryspinning of continuous filaments and, more particularly, to an improved method and means to provide a substantially uniform temperature during extrusion.

BACKGROUND OF THE INVENTION In the dry-spinning of synthetic fibers, temperature of the solution being spun is an important variable. It influences both viscosity of the solution and initial rate of evaporation of solvent from the extruded filaments. It is common practice to maintain temperature of the solution as low as practicable until just before extrusion, in the interest of low discoloration of the polymer it contains. A heater is provided just upstream from the point of extrusion to adjust the solvent temperature to that desired for best performance. The periphery of the extrusion apparatus is exposed at its lower extremity to entering hot gas employed to carry away solvent evaporated from the filaments. This gas may be 100 to 200 C. hotter than the solution, as is generally described in the Flannagan US. Patent 2,615,198. This exposure results in an undesirable solution temperature gradient from a low near the center of the spinneret to a high near its periphery. Thus, the outer filaments are extruded from solution of measurably higher temperature than that from which the center filaments are produced.

Several means have been employed to minimize the solution temperature differential. Insulation of the portion of the extrusion apparatus which projects into the hot gas is one obvious expedient; difficulty is encountered, however, due to the very limited space available and the need to maintain access to the spinneret for routine servicing and change. Gas deflectors are used, but these are not very etficient.

, A convenient means for reducing the solution temperature gradient across the face of the spinneret would be highly desirable.

SUMMARY OF THE INVENTION This invention provides method and means for maintaining uniform temperature of a fiber-forming solution across the spinneret employed in dry-spinning of synthetic filaments. It further provides method and means for extending control of solution temperature to a point just behind the spinneret employed to shape synthetic filaments. It still further provides method and means to extrude a synthetic polymer solution into a hot gas with substantially no variation in solution temperature. It also provides method and means to these advantages which utilizes conveniently available heat-exchange media.

3,509,244 Patented Apr. 28, 1970 These and other advantages are provided in the method of this invention which provides an improvement in the process for dry-spinning of continuous filaments which comprises the equalizing of the temperature of the extrusion zone by heat removal provided through the use of a volatile liquid substantially at its boiling point under regulated pressure in channels near the extrusion zone.

The improvement in apparatus, also provided by this invention, comprises such heat removal means within said spinneret assembly to equalize the temperature of the extrusion means.

PREFERRED EMBODIMENTS OF THE INVENTION The polymer solution may be heated in various ways. The mode shown in the drawing, in which the solution is heated by transfer of heat from a condensable gaseous heat exchange medium, is preferred. As described in greater detail hereinafter, the polymer solution is preferably heated by being brought in contact with a hot conden's'able, gaseous heat exchange medium (e.g., the poly mer solution is passed through a conduit which is surrounded by the heat exchange medium). The heat exchange medium is preferably saturated steam at a regulated pressure, the temperature of which is substantially equal to the desired polymer solution temperature. As the steam condenses, its latent heat of condensation provides sensible heat to the polymer solution. The design of the heat-exchanger is preferably such that both the exiting polymer solution and the condensate are substantially at the boiling point of the condensate (i.e., the temperature of the saturated steam at that pressure). The preference for this type of polymer solution heating is due, .in part, to the use of the condensate therefrom to equalize the extrusion zone temperature, as will'be further discussed hereinafter.

The solution streams may be extruded in a variety of patterns. A preferred pattern is a concentric cylindrical array of solution streams which may be obtained from a circular spinneret having orifices arranged in concentric circles. Conveniently, in a preferred embodiment, the hot gas evaporative medium is elevated to the desired temperature by a suitable heat-exchanger and brought into contact with the extruded streams as a non-turbulent, co-current stream from above the spinneret. This means avoids damaging transverse dislocation of the as-yet unsolidified filaments but entails continuous contact between the incoming hot gas and the periphery of the spinneret. Thus, a positive temperature gradient is established from center-to-periphery of the spinneret (due to the greater amounts of heat being transferred from the hot gas to the peripheral portions of the circular spinneret). The particular type of extrusion of spinneret plate, the shape of the orifices, etc., are not critical aspects of this invention; many suitable variations may be made.

The invention is well suited to the dry spinning of acrylic, spandex, vinyon, and cellulosic fibers as well as other polymers which are suitable for dry spinning. The inert solvent used to make up the polymer solution must of course be a solvent for the particular polymer and be volatile. The choice of solvent for a given polymer is based upon considerations such as solvent power, boiling point, heat of evaporation, stability, toxicity, ease of recovery, etc., as is well understood by those skilled in the art. Similarly the choice of hot gas employed to evaporate the solvent is based in part upon the particular polymer and solvent used; air, steam, or an inert gas are commonly employed. It is preferred that the gas employed be hotter than the extruded solution. (Generally, the gas should be at least about C. to 200 C. hotter.) In a preferred embodiment of this invention wherein acrylic fibers are prepared, the solvent preferably employed is 3 dimethylformamide and the gas a mixture of about 87% nitrogen and 13% carbon dioxide.

The invention is also suitable for spinning two or more fiber-forming polymers simultaneously such as different acrylic polymers or an acrylic and a spandex polymer. The solvent employed must be a suitable solvent for the particular polymer which may require the use of a different solvent for each polymer.

As previously noted, the solution temperature is an important variable in the dry-spinning of synthetic fibers. Once the desired temperature is chosen, any deviation from it is detrimental to best operation of the process. As previously described, the spinneret can absorb heat from the hot gas. It may also be heated by radiation from the spinning cell walls. In either case, the periphery is affected more than the center. The heat removal means of this invention provides a volatile liquid at its boiling point under regulated pressure which removes heat by vaporizing. In a most preferred embodiment for heat removal, this heat removal means is coupled with the means that was used to heat the polymer solution (preferably the condensable gaseous heat exchange medium previously described). The condensate from such medium is provided in conduits near the extrusion zone (e.g., behind the spinneret) under regulated temperature and pressure. If portions of the extrusion zone are at a temperature higher than the boiling point of the condensate, sensible heat is removed from the extrusion zone and transferred to the condensate providing the latent heat to vaporize it. Such vapor either recycles to the solution heater or is removed along with the unvaporized condensate by the condensate-return system for revaporization and recycling. This preferred heat removal is both simple and economical. The simplicity is seen in that only regulation of the pressure of the steam or other heat exchange medium is required to heat the polymer solution to the desired temperature; the condensate, autogenously maintained at that same pressure and at substantially the temperature of the solution, removes heat from the extrusion zone to assure extrusion at that desired temperature. The great advantage of such simplicity will be apparent to those skilled in the art, especially for commercial uses in 'which proper control of process variables is generally quite complex. The outstanding 'eco nomic advantage in such simplicity, coupled with the use of the same heat transfer means to both supply heat at one point and to remove heat at another, is also significant.

The positioning of the heat transfer means in the spinneret assembly is not critical and is generally dictated by the physical form of the equipment construction. For best results, the volatile liquid conduits must be positioned as near as possible to the portions of the extrusion zone which are heated to a greater degree by the hot gas. The desired goal is to minimize the temperature gradient, and the positioning of the transfer means is designed to achieve this goal. If the transfer means is not optimally positioned, it may be inadequate to reduce the temperature gradient to the desired degree. The exact positioning depends upon factors such as the thermal conductivity of the equipment, the temperature differential between the extrusion zone and the heat removal means, etc. Routine experimentation will determine the optimum positioning for a particular embodiment. It is preferred that such conduits be positioned above the spinnerets (preferably in the pack body), behind the peripheral portions of each spinneret. By use of automatic valve means available in the art, the condensate return may be interrupted briefly as the spinneret is removed (e.g., for cleaning) without disrupting the heat transfer system sufiiciently to affect adjacent spinning positions.

DESCRIPTION OF DRAWINGS In the drawing, FIGURE 1 is a schematic, cross-sectional elevation view of a spinning head such as used in this invention and FIGURE 2 is a cross-sectional plan view of the same assembly taken at plane 2-2.

With reference to the figures, solution from source not shown is delivered to solution heater, illustrated for simplicity as a straight conduit 10, during passage through which it is brought to near-equilibrium with the temperature of a condensable, gaseous heat exchange medium from source not shown which enters space 11 through inlet 12. Condensate partially fills space 11 and flows through inlet tube 13 which projects below the level of outlet tube 16 into channels 14 in pack body 15. Channels 14 provide the heat removal means as the condensate then proceeds therethrough. The generated vapor and unvaporized condensate flow to outlet tube 16 and upwardly to weir 17 from which it is delivered through dip tube 18 through a trap not shown to the condensate return system also not shown. It will be apparent that the design of this apparatus will effectively prevent vapor-locking, by means of the weir which surrounds the condensateremoval dip tube and by means of the difference in elevation between the inlet and the outlet tubes, 13 and 16, respectively. It is also not critical to maintain any particular level of condensate outside the weir, since the temperature of the condensable heat exchange fluid and its condensate will be essentially the same in an operating process.

Spinning solution from conduit 10 flows in contact with pack body 15 and through filter pack 19, which is supported by distributor plate 20, to a multiplicity of channels 21 to spinneret 22 where it is shaped to filaments of solution.

Hot gas, from source not shown is delivered through conduit 23 to gas-distributor chamber 24, which is in sulated from the solution heater as shown, and from which it flows through turbulence-suppressing means illustrated at perforated plate 25 and screen 26 to contact the freshly spun filaments of solution. The filaments lose the bulk of the solvent to the hot, evaporative medium as they progress through the spinning cell not shown, postioned below FIGURE 1, and are withdrawn at a carefully regulated speed for subsequent processing including extraction of the residual solvent, drawing, drying, etc. These steps are well-known in the art and need no detailed presentation here.

By utilizing the improvement of this invention, control of solution temperature is maintained substantially to the point of extrusion into the hot cell gas by equalizing the temperature across the spinneret, resulting in substantially uniform temperatures of all solution streams as extruded.

Those skilled in the art will recognize many departures from the specific design features of the illustrated embodiment which are within the spirit and scope of this invention. More rapid heating of solution will be attained in apparatus having an annular conduit for solution such that a thin film of solution flows between two surfaces heated by the same medium. It will also be seen that this invention is adaptable to apparatus for spinning of multi-component filaments, such as is described in the Breen US. Patent 3,038,236, for example.

It is understood, therefore, that the invention is not to be limited by the features of the described embodiment, but only by the claims which follow.

What is claimed is:

1. In a process for dry-spinning of continuous filaments comprising extruding streams of a heated acrylic polymer solution through an extrusion zone and contacting the extruded stream with a heated evaporative medium to evaporate solvent therefrom, wherein said heated evaporative medium transfers greater amounts of heat to various portions of said extrusion zone, the im provement which comprises:

(1) removing heat from said portions of said extrusion zone by providing a volatile liquid at its boiling point under regulated pressure near said portions of said extrusion zone, and

(2) removing vapors created by the evaporation of said volatile liquid to equalize the temperature of said extrusion zone.

2. The improved process of claim 1 wherein said acrylic polymer solution is heated, prior to extruding, by contact with saturated steam under regulated'pressure, and the condensate of said saturated steam being said volatile liquid provided for said removing of heat.

3. The improved process of claim 2 further comprising recycling the removed vapors.

4. In a spinneret assembly for use in the dry-spinning of continuous filaments by extruding streams of polymer solution through an extrusion plate, the improvement, utilizing a volatile liquid at its boiling point under regulated pressure, which comprises:

channels in said spinneret assembly near said extrusion plate for containing said volatile liquid, said channels operably connected to inlet means for supplying the volatile liquid thereto and outlet means for the removal of vapor therefrom to equalize the temperature of said extrusion plate.

5. The improved spinneret assembly of claim 4 wherein said extrusion plate is substantially circular in cross-section and said channels are positioned above the peripheral portions of said extrusion plate.

6. In an apparatus for use in the dry-spinning of continuous filaments comprising polymer-solution heating means to heat synthetic polymer solution to a substantially uniform temperature, a spinneret assembly having extruding means to extrude streams of heated synthetic polymer solution to form continuous filaments thereof, and evaporating means to contact the extruded solution streams with a heated evaporative medium to evaporate solvent therefrom, wherein said evaporative medium is heated to a temperature greater than the temperature of said polymer solution and said evaporative medium transfers greater amounts of heat to portions of said extruding means, the improvement, utilizing a volatile liquid at its boiling point under regulated pressure, which comprises:

channels in said spinneret assembly near said portions of said extrusion plate for containing said volatile liquid, said channels operably connected to inlet means for supplying the volatile liquid thereto and outlet means for removing vapor therefrom,

to equalize the temperature of said extruding means.

7. The improved apparatus of claim 6 wherein said extruding means is substantially circular in cross-section and said channels are positioned above the peripheral portions of said extrusion plate.

8. The improved apparatus of claim 7 wherein said polymer solution heating means is a condensable gaseous heat exchange medium and said volatile liquid is the condensate of said condensable gaseous heat exchange medium.

References Cited UNITED STATES PATENTS 2,367,493 1/1945 Fordyce et al. 264203 X 2,425,782 8/1947 Bludworth et al. 264203 2,463,676 3/1949 Bludworth et al. 264-203 2,948,584 8/1960 Euler et a1 264206 2,975,022 3/1961 Euler et a1 264206 3,410,940 11/1968 Henderson et al. 264182 3,415,922 12/1968 Carter et al. 264176 X JULIUS FROME, Primary Examiner I. H. WOO, Assistant Examiner US. Cl. X.R. 

